Utility companies have made various attempts to control the parameters of power being input into their utility systems by synchronizing this input power with the characteristics of the power already on the utility system. The ability to synchronize incoming power may become increasingly important as utility companies accept power from non-linear systems, such as rooftop solar arrays or batteries located at the edge of the utility system.
When DC (direct current) power is converted to AC (alternating current) power and transmitted to the utility system, the conversion process may introduce harmonics into the resulting AC power signal. In some instances, the power associated with these harmonics may represent up to 50% or more of the total power to be delivered to the utility system, but the power associated with the harmonics cannot be used by the utility. In addition, introducing harmonics into the utility system may damage components within the utility system.
Utility companies have attempted to implement various techniques to prevent harmonics from entering the utility system. One of those techniques involves filtering the power being delivered to the system to remove the harmonic signals. Utility companies have traditionally used switches to implement filters because the switches can handle the high energy and high current present on a utility system. Filtering using switches, though, has drawbacks. For example, filters built from switches do not closely match the frequencies of certain harmonics, such as the third and the fifth harmonics, and thus provide only a limited capability for removing these harmonics from the signal. In addition, switches may introduce new harmonics into the signal. In some situations, a switch-based filter may introduce the seventh harmonic into the signal even as it attempts to filter the third and the fifth harmonics. Furthermore, switches used by power utility companies are expensive, thus further detracting from their widespread use by utility companies.